Transmission means for use in torque and impulse transmitting machines

ABSTRACT

A portable torque and impulse transmitting machine wherein the output shaft of an electric motor carries two coaxial gears. One of the gears drives a first transmission which rotates the holder for a rotary tool, and the other gear transmits torque to a second transmission serving to oscillate an impeller which transmits impulses to the tool holder to thereby promote the penetration of the rotating tool into a wall or the like. One of the gears is integral with the output shaft and its modulus and the number of its teeth may, but need not differ from the modulus and the number of teeth of the other gear.

Waited States Patent [191 'llah'ner et al.

TRANSMISSION MEANS FOR USE IN TORQUE AND IMPULSE TRANSMITTING MACHINESInventors: Reinhard Hahner', Stuttgart; Wolfgang Schmid, Plattenhardt,both of Germany Robert Bosch GmbH, Stuttgart, Germany Filed: June 25,1971 ApplJNo.: 156,735

Assignee:

Foreign Application Priority Data References Cited UNITED STATES PATENTS8/1965 McCartyetal ..173/117 [451 May 29, 1973 3/1969 Miller ..l73/l l7Primary Examiner-James A. Leppink AttorneyMichael S. Striker [57]ABSTRACT A portable torque and impulse transmitting machine wherein theoutput shaft of an electric motor carries two coaxial gears. One of thegears drives a first transmission which rotates the holder for a rotarytool, and the other gear transmits torque to a second transmissionserving to oscillate an impeller which transmits impulses to the toolholder to thereby promote the penetration of the rotating tool into awall or the like. One of the gears is integral with the output shaft andits modulus and the number of its teeth may, but need not differ fromthe modulus and the number of teeth of the other gear.

8 Claims, 1 Drawing Figure 2/1969 Germany ..173/1o4 TRANSMISSION MEANSFOR USE IN TORQUE AND IMPULSE TRANSMITTING MACHINES BACKGROUND OF THEINVENTION The present invention relates to improvements in transmissionmeans for use in torque and impulse transmitting machines, particularlyto improvements in transmission means for use in portable power tools,

such as hammer drills, impact wrenches or the like.

ler by way of a first power train and to rotate the toolby way of asecond power train. The two power trains have avcommon inputmember'which is a gear meshing with the gear or pinion on the outputshaft. A drawback of such machines is that a single tooth on the gear orpinion of the output shaft must stand all stresses,

namely, the stresses which arise as a result of movements of theimpeller as well as the stresses which develop as .a result oftransmission of torque to the tool. Also, the number of gears in suchmachines is very large and the two power trains occupy a large amount ofspace.

It is further known to place the pinion on the output shaft of the motorin a portable torque and impulse transmitting machine into mesh with twodiscrete gears one of which forms part of the power train for theimpeller and the other of which transmits torque to the. too]. Anadvantage of such machines is that the stresses which arise as a resultof reciprocatory movements of the impeller are taken up by one tooth andthe stresses which arise as a result of rotary movement of the tool aretaken up by another tooth of the pinion on the output shaft. However,such machines still exhibit a serious drawback which is also shared bythe first type of conventional machines, namely, that the highfrequencyoscillatory movements of the impeller must be derived from the samepinion which serves to impart .to the tool a relatively slow rotarymovement. As a rule,

the average torque which is required to oscillate the impeller exceedsat least three times the magnitude of torque which is needed to rotatethe tool. Furthermore, a single tooth of the pinion on the output shaftof the motor must take up extremely high but short-lasting stresseswhich arise during each cycle of oscillatory movement of the impeller,namely, during maximum acceleration of the'impeller. Therefore, theteeth of the pinion must be designed to stand substantial torque whichmust be transmitted to the transmission for the impeller and thestresses which arise due to the large step-down ratio of the drive forthe rotary tool. As a rule, the design of teeth on the pinion is acompromise which can stand very high bending stresses whereas theoptimum step-down transmission for rotating the tool necessitates theprovision of a pinion which exhibits other desirable characteristics.

SUMMARY OF THE INVENTION An object of the invention is to provide aportable power-operated torque and impulse transmitting machine, such asa hammer drill, with novel and improved transmission means which isideally suited for transmission of reciprocatory movements to theimpeller and is also best suited for transmission of torque to the tool.

Another object of the invention is to provide a machine of the justoutlined character with novel means for driving two discrete powertrains, namely, a power train which reciprocates the impeller and apower train which rotates the tool.

A further object of the invention is to provide the prime mover of amotor in a portable torque and impulse transmitting machine with a noveloutput shaft.

An additional object of the invention is to provide the machine withnovel means for transmitting motion from the output shaft of the motorto two discrete power trains.

The improved torque and impulse transmitting machine comprises a housingor body, an electric motor or another suitable prime mover mounted inthe housing and having a' rotary output shaft, an impact receiving toolholder which is rotatably mounted in the housing, a pair of coaxialgears provided on the shaft of the prime mover, first transmission meanshaving a rotary input member meshing with one of the gears on the shaftand an output member arranged to rotate the tool holder, impeller meansmovable into and from impulsetransmitting engagement with the toolholder, and second transmission means having a rotary input membermeshing with the other gear on the output shaft and output meansarranged to move the impeller means in response to rotation of theoutput shaft.

The number of teeth on one of the gears may but need not be differentfrom the number of teeth on the other gear, and the same applies for themoduli of the two gears. One of the gears may constitute a pinion whichis integral with the output shaft of the prime mover, and the diametersof the input members of the two transmission means preferably exceed thediameters of the respective gears on the output shaft.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved transmission means itself, however, both as to its constructionand its mode of operation, together with additional features andadvantages thereof, will be best understood upon perusal of thefollowing detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a fragmentarycentral sectional view of a portable impulse and torque transmittingmachine which embodies the improved transmission means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing illustrates aportable power-operated tool, for example, a hammer drill, whichcomprises a housing 1 having a handle, not shown, and surrounding aprime mover 3a (such as an electric or pneumatic motor). The outputshaft 3 of the prime mover 3a is rotatable in a needle bearing 2provided therefor in the housing 1. In accordance with a feature of theinvention, the output shaft 3 can rotate two discrete gears, namely, afirst gear 4 which preferably constitutes an integral pinion of theshaft 3 and a ring-shaped second gear 7 which is adjacent to the outeraxial end of the gear 4. The output shaft 3 has a cylindrical portion 5of reduced diameter which extends forwardly beyond the gear 4 and issurrounded by the ring-shaped gear 7 which is held thereon againstrotation and against axial movement by an internally threaded member 8(e.g., a nut) which meshes with the externally threaded portion or tip 6of the shaft 3. The diameter of the cylindrical portion 5 is slightlysmaller than the pitch circle of the gear 4 so that the front end faceor shoulder 4 a of the gear 4 serves as an abutment for the adjacentrighthand end face of the gear 7. The other end face of the gear 7 is inabutment with the right-hand end face of the nut 8. The right-hand endface of the nut 8, the end face 4a of the gear 4 and the two end facesof the gear 7 are located in planes which are normal to the axis of theshaft 3. The gear 7 has helical teeth and its righthand end face isbiased against the end face 4a of the pinion 4 by the nut 8.

The housing 1 further supports a rotary tool holder TH for a boring ordrilling tool T. The tool holder TH is rotatable with reference to thehousing 1 by a first transmission which receives torque from the gear 4and includes a large-diameter gear 9 which constitutes the input memberof the first transmission and forms the first element of a gear trainhaving an output member 9a slidably mounted on the tool holder TH. Thefirst transmission further includes a safety clutch 10 one element ofwhich is driven by the gear 9 and another element of which drives a stubshaft 1 1 for a bevel gear 12. The latter meshes with a conical ringgear forming the output member 9a of the first transmission-The stubshaft 11 is rotatable in an antifriction ball bearing 13 which ismounted in the housing 1 and the clutch 10 is mounted in a needlebearing 14.

The illustrated machine further comprises a second transmission having alarge-diameter input member or gear 15 which meshes with the gear 7 onthe output shaft 3. The input member 15 is rigid with a stub shaft 16which is mounted in two coaxial needle bearings 17 provided therefor inthe housing 1. The input member 15 has an eccentric crank pin 18 whichis surrounded by a needle bearing 19 and extends into a transverselyextending guide slot 22 provided in a slide 20 which is reciprocable inparallelism with the axis of the tool holder TH. The slide 20 is rigidlyconnected to or integral with a cylinder 21 which constitutes the outputmember of the second transmission and serves to reciprocate an impeller23 which can transmit impulses to the tool holder TH to thereby drivethe tool T into a wall or the like while the tool rotates in response torotation of the output member 9a of the first transmission. The guideslot 22 is normal to the direction of reciprocatory movement of thecylinder 21 and such direction is normal to the axes of the shafts 3, 11and 16. The cylinder 21 is provided with a chamber 24 located behind therear end face 25 of the impeller 23 and filled with a gas which iscompressed during a first stage of forward (downward) movement of thecylinder 21 under the action of the crank pin 18 to thereupon acceleratethe impeller in a direction toward the tool holder TH. The manner inwhich the impeller can transmit impacts to the tool holder TH and inwhich the tool holder can be rotated by the first transmission ispreferably similar to that disclosed in the copending application Ser.No. 99,931 filed Dec. 21, I970 by Karl Wanner et al., and assigned tothe owner of the present application.

An important advantage of the illustrated machine is that the first andsecond transmissions which respectively serve to rotate the tool holderTH and to transmit to the tool holder a rapid succession of impulsesreceive torque from two discrete gears 4, 7 on the output shaft 3. Thegear 4 can have a small modulus and a relatively small number of teethwhich is best suited for the large step-down ratio of the firsttransmission which requires a small torque. The modulus and the numberof teeth on the gear 7 may but need not be different from thecorresponding characteristics of the gear 4; however, they are selectedwith a view to insure that the gear 7 is best suited to transmit torqueto the second transmission which must transmit a higher torque. Sincethe gear 7 constitutes a discrete element, its modulus and the number ofits teeth can be selected independently of the modulus and number ofteeth on the gear 4. Another important advantage of the improved machineis that the wear is distributed between two discrete gears 4, 7 and thatpermanent bending stresses upon the output shaft 3 are also shared bytwo gears. This renders it possible to insure optimum conditions forlong-lasting use of the machine and to provide on the shaft 3 twodiscrete gears which are best suited to drive the input members 9, 15 ofthe respective transmissions. It will be noted that the diameters of theinput members 9, 15 substantially exceed the diameters of the respectivegears 4, 7 on the output shaft 3. The prime mover 3a of the machine ispreferably an electric motor.

The provision of the removable gear 7 in front of the gear 4 which isintegral with the output shaft 3 facilitates the assembly anddismantling of the machine. The assembly is further facilitated if thecylindrical portion 5 of the output shaft 3 is shorter than the gear 7and if the latter is rotatable and axially movable on the cylindricalportion 5 of the shaft 3 prior to tightening of the nut 8. Owing to suchdimensioning of the shaft portion 5 and gear 7, the latter is held instrong frictional engagement with the end face 4a of the gear 4 when thenut 8 is driven home because the nut is caused to move into strongfrictional engagement with the left-hand end face of the gear 7 by thegear 7 itself which by its helical teeth is biased against the nut 8.The shaft 3 and/or the shaft 16 is preferably rotatable in a singledirection. If the shaft 3 is rotatable in a counterclockwise direction,seen on its end face, the gear 7 has teeth with right-hand helices, andvice versa. Also, if the shaft 3 is rotatable in a counterclockwisedirection, seen on its end face, the threads of the nut 8 formright-hand helices, and vice versa.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art and, therefore, suchadaptations should and are intended to of one end a cylindrical portionof reduced diameter forming with the remainder of said shaft a shoulderat one of end of said cylindrical portion and an external threadedportion on the other end of said cylindrical portion; impulse-receivingtool holder means rotatably mounted in said housing; a pair of coaxialgears on said shaft, one of said gears being fixedly mounted on theremainder of said shaft and the other gear being a helical gear mountedwith a slide fit on said cylindrical shaft portion and having a axiallength slightly longer than that of said cylindrical portion; aninternally threaded member screwed on to said externally threaded shaftportion so as to press said other gear against said shoulder, saidoutput shaft being rotatable only in one direction and the teeth of saidhelical gear and the threads of said internally threaded member forminghelices in a direction so as to tighten the pressure on the shoulderduring turning of said output shaft in said one direction; firsttransmission means having a rotary input'member meshing with-said onegear and an output member arranged to rotate said rotary tool holdermeans; impeller means movable into and from impulse transmittingengagement with said tool holder means; and second transmission meanshaving a rotary input member meshing with said other gear and outputmeans arranged to move said impeller means in response to rotation ofsaid last mentioned input memher.

2. The combination of claim 1, wherein the number of teeth on one ofsaid gears differs from the number of teeth on the other gear.

3. The combination of claim 1, wherein the modulus of one of said gearsdiffers from the modulus of the other gear.

4. The combination of claim 1, wherein one gear is integral with saidshaft.

5. The combination of claim 4, wherein the diameters of said inputmembers exceed the diameters of the respective gears on said shaft.

6. A combination as defined in claim 1, said externally threaded portionof said output shaft being coaxial with said cylindrical portion andhaving a diameter which at most equals the internal diameter of saidother gear.

7. A combination as defined in claim 1, wherein said output shaft isrotatable in a counterclockwise direction, seen on its end face, theteeth of said other gear and the threads of said internally threadedmember forming right-hand helices.

8. A combination as defined in claim 1, wherein said output shaft isrotatable in a clockwise direction, seen on its end face, the teeth ofsaid last mentioned gear and the threads of said internally threadedmember forming left-hand helices.

1. In a torque and impulse transmitting machine, particularly in aportable torque and impulse transmitting power tool, a combinationcomprising a housing; a prime mover mounted in said housing and having arotary output shaft, said output shaft having in the region of one end acylindrical portion of reduced diameter forming with the remainder ofsaid shaft a shoulder at one of end of said cylindrical portion and anexternal threaded portion on the other end of said cylindrical portion;impulsereceiving tool holder means rotatably mounted in said housing; apair of coaxial gears on said shaft, one of said gears being fixedlymounted on the remainder of said shaft and the other gear being ahelical gear mounted with a slide fit on said cylindrical shaft portionand having a axial length slightly longer than that of said cylindricalportion; an internally threaded member screwed on to said externallythreaded shaft portion so as to press said other gear against saidshoulder, said output shaft being rotatable only in one direction andthe teeth of said helical gear and the threads of said internallythreaded member forming helices in a direction so as to tighten thepressure on the shoulder during turning of said output shaft in said onedirection; first transmission means having a rotary input member meshingwith said one gear and an output member arranged to rotate said rotarytool holder means; impeller means movable into and from impulsetransmitting engagement with said tool holder means; and secondtransmission means having a rotary input member meshing with said othergear and output means arranged to move said impeller means in responseto rotation of said last mentioned input member.
 2. The combination ofclaim 1, wherein the number of teeth on one of said gears differs fromthe number of teeth on the other gear.
 3. The combination of claim 1,wherein the modulus of one of said gears differs from the modulus of theother gear.
 4. The combination of claim 1, wherein one gear is integralwith said shaft.
 5. The combination of claim 4, wherein the diameters ofsaid input members exceed the diameters of the respective gears on saidshaft.
 6. A combination as defined in claim 1, said externally threadedportion of said output shaft being coaxial with said cylindrical portionand having a diameter which at most equals the internal diameter of saidother gear.
 7. A combination as defined in claim 1, wherein said outputshaft is rotatable in a counterclockwise direction, seen on its endface, the teeth of said other gear and the threads of said internallythreaded member forming right-hand helices.
 8. A combination as definedin claim 1, wherein said output shaft is rotatable in a clockwisedirection, seen on its end face, the teeth of said last mentioned gearand the threads of said internally threaded member forming left-handhelices.